The present application claims priority of Russian Application Serial No. 98/10/0569 filed Jan. 5, 1999, entitled xe2x80x9cMAGNETRONxe2x80x9d, which in turn claims priority from Russian Application Serial No. 98/10/0560 filed Jan. 5, 1999, entitled xe2x80x9cM-TYPE MICROWAVE DEVICExe2x80x9d the disclosures of which are incorporated by reference herein in their entirety.
The present invention relates generally to the field of electronics and, more particularly, to vacuum electron devices intended to generate microwave electromagnetic radiation using an electron-transit time, namely to magnetrons.
In particular, the present invention relates to structural elements of magnetrons, namely to cathodes requiring no preliminary incandescence to perform electron emission. Especially, this invention relates to magnetrons with a low readiness time.
Magnetrons comprising a cylindrical anode with evacuated internal and resonant cavities and a cathode disposed co-axially inside the anode, the cathode having focusing shields located on its end-faces and facing with their inner surfaces, a magnetron internal cavity, are known and widely used to generate microwave radiation.
There are commonly used cathodes making use of a combination of secondary electron emission caused by return to a cathode of a part of electrons travelling in the inter-electrode space along epicycloids, as well as ion bombardment with respect to the cathode, and field emission, i.e., the phenomenon of electron ejection from a conductor surface under the action of a fairly strong electric field, which initiates and sustains the secondary electron emission. A cylindrical cathode body which is co-axial with an anode is fabricated from material having improved secondary-emission properties.
A required quantity of field emission is primarily afforded by the shape of corresponding elements, in particular by their fabrication in the form of a sharpened element, and their location relative to cathode sections with secondary-emission properties. Thus, location of a field-emitter on a focusing flange to diminish a destructive effect of electron bombardment exerted on said cathode sections is known from USSR Inventor""s Certificate No. 320,852 granted Nov. 4, 1971 to L. G. Nekrasov et al., for xe2x80x9cCathode For M-Type Microwave Devicexe2x80x9d, Int. Cl. H01J 1/32.
RU Patent No. 2,051,439 granted Dec. 27, 1995 to V. I. Makhorv et al., for xe2x80x9cMagnetronxe2x80x9d, Int. Cl. H01J 1/30, describes a magnetron comprising a cylindrical anode and a cathode composed of a secondary-electron emitter, focusing flanges whose apertures are provided with field-electron emitters isolated from the flanges, the field-electron emitters inducing a primary current to activate the magnetron. The design of this magnetron and operating principle of such design constitute the closest prior art with respect to the present invention.
The opportunity for field-electron emitters in this design to be at potential other than potential of secondary-electron emitters, made it possible to attain improvements in the, magnetron starting and operating effectiveness. At the same time, a cantilever attachment of field-electron emitters requires a significantly higher mounting accuracy and restricts possibilities of using this design under vibration conditions.
The principal objects of the present invention are: to improve effectiveness of using a working surface of a field-electron emitter, to simplify the design; and to improve mechanical strength and reliability of the magnetron, while ensuring protection from microwave radiation.
According to the present invention, these objects are solved in a magnetron comprising a cylindrical anode with evacuated internal and resonant cavities and a cathode assembly disposed co-axially inside the anode, the cathode assembly comprising a cylindrical secondary-electron emitter which is co-axial with the anode; a field-electron emitter made in the form of a sharpened element; and a pair of focusing shields located on the end-faces of the cathode assembly and defining along the anode and the secondary electron emitter, an evacuated resonant cavity. In this arrangement, the focusing shields (or at least one of them) are electrically isolated from the secondary-electron emitter, and the field-electron emitter is located on the inner surface of such focusing shield.
In one preferred embodiment of the present invention, the field-electron emitters are provided on their working end-faces with projections.
For a number of practical applications, a lateral surface of the field-electron emitter may be developed at random (may be corrugated, may have folds or projections, etc.).
In a preferred embodiment of the present invention, the ends of a secondary-electron emitter cylinder (or at least one of those ends) underlying a field-electron emitter end-face are made in the form of truncated cone with its inclined surface facing a vacuum gap between the anode and the cathode.
In another preferred embodiment of the present invention, the ends of the secondary-electron emitter cylinder (or at least one of those ends) underlying a field-electron emitter end-face are provided with notches to accommodate projections of the field-electron emitter.
In still another preferred embodiment of the present invention, a secondary-electron emitter region underlying a field-electron emitter end-face is coated with a film made of foreign material. Such a material is selected from the group consisting of metals, alloys, semiconductors and dielectrics having a secondary electron-emission coefficient greater than that of the secondary-electron emitter material.
Essential distinctions of the proposed magnetron consist in the electrical isolation of the focusing shield from the secondary-electron emitter and provision of such shield with the field-electron emitter whose working end-face-faces the surface of the secondary-electron emitter.
This distinctive feature gives rise to the solution of objectives in accordance with the present invention. In doing so, the primary current increase is attained at the expense of more efficient usage of the working surface of field-electron emitters, since, in accordance with the present arrangement, emission occurs from the larger surface of the film emitter.
An additional advantage of the present invention consists in the increase of a field emission current at the expense of possibility to use two focusing shields having the field-electron emitters and electrically isolated from the secondary-electron emitter.
The third advantage of the present invention consists in the possibility to step down the operating voltage of the device triggering by decreasing a gap between field-electron and secondary-electron emitters, while affording improvements in the screening properties of the focusing shields from microwave radiation, expansion of types of devices used and structural capabilities of field-electron emitters and employment of a wider range of materials and alloys, providing high secondary-electron emission coefficients, stability of volt-ampere characteristics and an extended service life of the devices.
Additional objects and advantages of the present invention will be set forth in the detailed description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.